[Tutor] Paper Rock Scissors game - User's choice not returned properly

[Joel Montes de Oca]

Hello everyone,

I am having a little trouble with a block of code that isn't behaving 
the way I would expect. Maybe you can give me a hand and point where it 
is going wrong.

The function that is not working correctly belongs to a Paper Rock 
Scissor game I am making.

This particular function is responsible to:
   a) Get the user's choice (Paper, Rock, or Scissors)
   b) Return the user's choice within the variable choice to the 
function that called it.

The function works correctly as long as the user _does not try to enter 
a string other than_ 'P', 'R', or 'S'.

Logic:
     Take the user's string and put it in the variable choice.
     If choice is not 'P', 'R', or 'S'then pass a message to the user 
and call the function again.
     If the choice is 'P', 'R', or 'S'then return choice to where it was 
called from.

The problem is this.

When the user enters a string other than the valid ones, the if 
statements catches it and calls the same function again so the user can 
enter a valid string. But the variable choice does not get assigned the 
new string entered by the user, instead it is empty.

I would expect if the function runs again, the variable choice would be 
updated to the last value given by the user.

The function: ( http://dpaste.com/644857/)

def  UserChoice  ():	# The function that returns the choice from the user
	print  'Please select (P) for paper, (R) for Rock, or (S) for Scissors.'
	choice  =  raw_input('What is your selection?:')

	if  choice.lower()  not  in  ('p',  'r','s'):	# Converts the user's choice to lowercase and confirms the choice is valid
		print  'I am sorry, you entered\''  +  choice.upper()  +  '\'  which is an invalid response. Please try again.'
		raw_input('Press Enter to try again.')
		UserChoice  ()		# If the choice is not valid, run the function over
	else:
		return  choice



Output with no problems: ( http://dpaste.com/644866/) 
<http://dpaste.com/644866/>

Welcome to the PRS game.

Please select (P) for paper, (R) for Rock, or (S) for Scissors.
What is your selection?: s

	You threw down Scissors while the computer threw down Rock

LOOSE

Output with problems: ( http://dpaste.com/644868/)

Welcome to the PRS game.

Please select (P) for paper, (R) for Rock, or (S) for Scissors.
What is your selection?: L
I am sorry, you entered 'L' which is an invalid response. Please try again.
Press Enter to try again.
Please select (P) for paper, (R) for Rock, or (S) for Scissors.
What is your selection?: s

	You threw down None while the computer threw down Paper

LOOSE

Here's the full source code in case the problem is outside of the 
function: ( http://dpaste.com/644873/)

import  random	# Import the random library

def  main  ():	# The main function that gets called from main()
	print  '\nWelcome to the PRS game.\n'

	choice  =  UserChoice  ()	# Gets the choice from the user
	cchoice  =  ComputerChoice  ()		# Gets the choice from the computer
	
	PrintOutcome  (choice,  cchoice)	# Passes both choices to the PrintChoice function for display


	return  0

def  UserChoice  ():	# The function that returns the choice from the user
	print  'Please select (P) for paper, (R) for Rock, or (S) for Scissors.'
	choice  =  raw_input('What is your selection?:')

	if  choice.lower()  not  in  ('p',  'r','s'):	# Converts the user's choice to lowercase and confirms the choice is valid
		print  'I am sorry, you entered\''  +  choice.upper()  +  '\'  which is an invalid response. Please try again.'
		raw_input('Press Enter to try again.')
		UserChoice  ()		# If the choice is not valid, run the function over
	else:
		return  choice

def  ComputerChoice  ():		# The function that returns the choice from the computer
	PRS  =  ['Rock',  'Paper',  'Scissors']		# A list of choices

	cchoice  =  random.choice(PRS)	# Choose a random item from the list

	return  cchoice		# Return the function

def  PrintOutcome  (UC,  CC):		# Function responsable to display the choices and results
	PRS  =  ['Rock',  'Paper',  'Scissors']
	
	# Convert the letters to words
	if  UC  ==  'r':
		UC  =  PRS[0]
	elif  UC  ==  'p':
		UC  =  PRS[1]
	elif  UC  ==  's':
		UC  =  PRS[2]
		
	print  '\n\tYou threw down',  UC,  'while the computer threw down',  CC  +'\n'
		
	# find the outcome of the game
	if  UC  ==  CC:
		print  'We have a tie, both players gain a point!'
	elif  UC  ==  'Rock'  and  CC  ==  'Scissors':
		print  'WIN'
	elif  UC  ==  'Paper'  and  CC  ==  'Rock':
		print  'WIN'
	elif  UC  ==  'Scissors'  and  CC  ==  'Paper':
		print  'WIN'
	else:
		print  'LOOSE'

	return  0

main()

I am using Python 2.7
I am running on Ubuntu 11.10

Thanks for any help

-- 
-Joel M.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/tutor/attachments/20111031/e16e2f16/attachment-0001.html>